This invention relates in general to a system for measuring radiance of radiation sources, and in particular, to luminance meters of improved performance, as well as other parameters such as transmittance and reflectance.
Luminance meters have wide applications. It is used, for example, in radiology for calibrating the intensity of radiation sources such as x-ray sources in order to be able to compare images for improve accuracy.
Conventional luminance meters employed circular apertures for passing radiation from the radiation source to the sensor. In such conventional luminance meters, due to the symmetry of the circular apertures employed, stray radiation has the maximum probability of reflection at the edges of the apertures to reach the sensor.
When a conventional luminance meter is employed to measure radiation sources with rapidly varying intensities, depending on the sampling time period chosen, the meter may give a reading that is widely different from that perceived from the human eye. For example, when the conventional luminance meter is employed to measure the radiance from a cathode array tube screen, for example, the radiance from the phosphor decays rapidly. Therefore, depending upon the sampling time period of the conventional luminance meter employed when the screen is measured, the radiance measured may be that from the phosphor after the intensity of the radiance has declined significantly, so that the reading given by the meter may differ from that observed by the human eye by a significant amount.
While conventional luminance meters may be adequate for some applications, they do not provide adequate dynamic range and resolution for other applications such as in radiology requiring higher performance. It is, therefore, desirable to provide improved luminance meters that can meet the needs of such other applications with higher performance requirements.